1. Field of the Invention
The present invention relates to a method and related communication device for determining a dedicate searching space of a physical downlink control channel, and more particularly, to a method and related communication device for determining a dedicate searching space of a physical downlink control channel in a user equipment (UE) of a wireless communication system, so as to reduce loading of blind decoding operation.
2. Description of the Prior Art
Long Term Evolution wireless communications system (LTE system), an advanced high-speed wireless communications system established upon the 3G mobile telecommunications system, supports only packet-switched transmission, and tends to implement both Medium Access Control (MAC) layer and Radio Link Control (RLC) layer in one single communication site, such as in Node B alone rather than in Node B and RNC (Radio Network Controller) respectively, so that the system structure becomes simple.
In LTE system, a user equipment (UE) performs blind decoding in a searching space of physical downlink control channel (PDCCH) to acquire control information which a network terminal schedules to the UE. Generally, two types of searching spaces in PDDCH are defined, common searching space (CSS) and UE-specific searching space. CSS is utilized for transmitting common messages such as paging, broadcast messages, power control messages or Random Access Channel (RACH) response messages, etc. UE-specific searching space, also called dedicate searching space (DSS), is utilized for transmitting messages dedicated to a UE.
CSS is composed of the first 16 control channel elements (CCEs), while a starting location of DSS is derived from a user equipment identifier (UE-ID) such as a cell radio network temporary identifier (C-RNTI), for example, and a CCE Aggregation Level. Regarding how the UE determines the starting location of DSS by the UE-ID and the CCE Aggregation Level, please refer to related technical specifications, and is not given herein.
On the other hand, LTE system has two scheduling methods: dynamic scheduling (DS) and semi-persistent scheduling (SPS) A common dynamic grant allocated by DS is addressed to the C-RNTI of the UE, while an SPS grant is addressed to an SPS C-RNTI of the UE. In other words, the UE monitors the C-RNTI and the SPS C-RNTI in PDCCH to acquire the common dynamic grant and the SPS grant, respectively. However, when the UE waits for the SPS grant, the UE has to monitor both the SPS C-RNTI and the C-RNTI since the Node B may schedule the common dynamic grant at the same time.
Therefore, when the UE wants to receive the SPS grant, the UE not only determines a location of a DSS for the SPS grant according to the SPS C-RNTI, but also determines a location of a DSS for blind decoding the common dynamic grant according to the C-RNTI. Under such circumstances, comparing to the operation that the UE only receives the common dynamic grant, the UE needs to perform blind decoding operations in two different DSSs, respectively, causing the loading of blind decoding increases.